Direct water vaporization for fuel processor startup and transients

ABSTRACT

A fuel cell system including a fuel reforming processor having a catalyst therein constructed and arranged to produce a reformate stream including hydrogen and carbon monoxide, a water gas shift reactor downstream of the fuel reforming processor and wherein the water gas shift reactor includes a catalyst therein constructed and arranged to reduce the amount of carbon monoxide in the reformate stream, a preferential oxidation reactor downstream of the water gas shift reactor and wherein the preferential oxidation reactor includes a catalyst therein constructed and arranged to preferentially oxidize carbon monoxide into carbon dioxide and to produce a hydrogen-rich stream, and a fuel cell stack downstream of the preferential oxidation reactor constructed and arranged to produce electricity from the hydrogen-rich stream, a first direct water vaporizing combustor constructed and arranged to combust fuel producing a high-temperature fuel combustion byproducts exhaust and to produce steam from water sprayed into the combustion byproduct exhaust and wherein the first direct water vaporizing combustor is plumbed to the fuel reforming reactor to charge steam therein, and a second direct water vaporizing combustor constructed and arranged to combust fuel to produce a high-temperature fuel combustion byproduct exhaust and to produce steam from water sprayed into the fuel combustion byproduct exhaust and wherein the second direct water vaporizing combustor is plumbed to the water gas shift reactor to charge steam therein.

CROSS REFERENCE TO RELATED APPLICATIONS

This is a Division Application of U.S. Application of U.S. applicationSer. No. 10/077,471filed Feb. 15, 2002, now U.S. Pat. No. 7,008,707.

TECHNICAL FIELD

This invention relates to a fuel processing system, and moreparticularly to a fuel processing system with direct water vaporizationfor fuel processor startup and transients in a fuel cell system.

BACKGROUND OF THE INVENTION

Many fuel cells use hydrogen (H₂) as a fuel and oxygen (typically in theform of air) as an oxidant. The hydrogen used in the fuel cell can beproduced from the reformation of fuels that include hydrogen (forexample, methanol or gasoline). The reforming of fuels that includehydrogen may be accomplished using a variety of techniques including:(1) steam reforming in which the fuel in gaseous form reacts with steam;(2) partial oxidation in which the fuel reacts with oxygen or air inproportions less than that needed for complete oxidation; or (3)autothermal reforming in which the fuel partially reacts with steam andpartially reacts with oxygen (or air) in a combination steam reformingand partial oxidation type reactor. Steam reforming is more efficient interms of the yield of hydrogen than partial oxidation. Steam reformingis endothermic while partial oxidation as exothermic. Autothermalreforming falls somewhere in between steam reforming and partialoxidation both in terms of hydrogen yield and the heat addition/removalrequired.

The selection of a particular reforming process depends upon theparticular operation and factors which include the hydrogen yieldrequired, equipment costs and complexity, and the overall process heatrequirements. Regardless of the type of fuel reforming reactor utilized,the reformate exiting the reactor typically includes undesirably highconcentrations of carbon monoxide which must be removed to preventpoisoning of the catalyst on the fuel cell's anode. The hydrogen-richreformate/effluent exiting the fuel reforming reactor typically includescarbon monoxide, in about 3-10 mole percent, that must be reduced tovery low concentrations, preferably less than 20 ppm, to avoid poisoningthe fuel cell anode catalyst.

It is known that the carbon monoxide level of the reformate/effluentexiting a fuel processing reactor can be reduced utilizing a “water gasshift reaction” (WGS) utilizing the excess steam present in thereformate exiting the fuel reforming reactor or wherein water in theform of steam is added to the reformate/effluent exiting the fuelreforming reactor in the presence of a suitable catalyst. This lowersthe carbon monoxide content in the reformate according to the followingideal water gas shift reaction:CO+H₂O→CO₂+H₂   (WGS)

About 0.5 mole percent or more CO still survives the water gas shiftreaction. The effluent exiting the water gas shift reactor includeshydrogen, carbon dioxide, water, carbon monoxide, and nitrogen.

The water gas shift reaction is a not enough to reduce the CO content inthe reformate to an acceptable level of about 20-200 ppm or less.Therefore, it is necessary to further remove carbon monoxide from thehydrogen-rich reformate stream exiting the water gas shift reactor priorto supplying the hydrogen-rich stream to the fuel cell. It is also knownto further reduce the CO of the hydrogen-rich reformate exiting thewater gas shift rector using a preferential oxidation (PrOx) reactionconducted in a reactor with a suitable catalyst and at a temperaturethat promotes the preferential oxidation of the CO with the O₂ (air) inthe presence of the H₂ but without consuming or oxidizing substantialamounts of H₂ or without triggering a “reverse water gas shift” (RWGS)reaction. The PrOx and RWGS reactions are as follows:CO+½O₂→CO₂  (PrOx)CO₂+H₂→H₂O+CO  (RWGS).

Preferably, the oxygen provided for the PrOx reaction will be about twotimes the stoichiometric amount required to react the CO in thereformate. If the amount of oxygen exceeds about two times thestoichiometric amount needed, excessive consumption of hydrogen results.On the other hand, if the amount of oxygen is substantially less thanabout two times the stoichiometric amount needed, insufficient COoxidation may occur and there is a greater potential for the reversewater gas shift (RWGS) reaction to occur. Therefore, it is typical forthe process to be conducted at about four or more times thestoichiometric amount of oxygen that is theoretically required to reactwith the CO.

PrOx reactors may be either (1) adiabatic wherein the temperature of thereactor is allowed to rise during oxidation of the CO, or (2) isothermalwherein the temperature of the reactors maintain substantially constantduring the oxidation of the CO. The adiabatic PrOx process is sometimesaffected via a number of sequential stages, which progressively reducesthe amount of CO in stages and requires careful temperature control sothat the temperature rise is not so great that the reverse water gasshift reaction occurs thereby undesirably producing more CO.

The fuel reforming process of gasoline or other hydrogen containingfuels typically occurs at high temperatures of about 600-800° C. orabove. The one notable exception is methanol which can be reformed attemperatures of about 400° C. The water gas shift reaction is typicallycarried out at a temperature of about 250-450° C. The PrOx reactiontypically occurs at about 100-200° C. Therefore, it is necessary for thefuel reforming reactor, the water gas shift (WGS) reactor, and the PrOxreactor to be heated to temperature sufficient for the system to operateproperly. However, during startup, conventional fuel processing requiresthe system components to be heated in stages. This approach leads to anundesirable lag time for bringing the system online. For example, inconventional fuel cell systems it is typical to use boilers, tube andshell type exchangers, or compact bar and plate type exchangers toproduce steam from water. These boilers or exchangers are massive andrequire a substantial amount of heat input to heat up the equipmentcomponents before heat can be transferred to the water to create steam.A substantial amount of lag time is thus associated with the use ofthese types of steam generating equipment. Furthermore, these heavyboilers or exchangers are a disadvantage in mobile applications such asvehicles which are powered at least in part by a fuel cell system.Because there is no direct contact between the combustion source in theboiler or the fluid in the tube and shell heat exchanger, these devicesproduce pure steam.

Alternatively, external electric heat sources may be employed to bringthe components to proper operating temperatures. This approach requiresan external electrical source such as a battery, which is heavy, anddraws electricity from the system that is designed to generateelectricity through the fuel cell. Furthermore, in conventional fuelprocessing and fuel cell systems, substantial increases on the fuel cellelectrical load demand requires rapid delivery of substantial amounts ofhydrogen to the fuel cell to accommodate the increase in electricaldemand. A substantial lag time has typically occurred in conventionalfuel cell systems attempting to respond to such transient conditions.

Therefore, it is desirable to provide a fuel processing system in a fuelcell system that is capable of rapidly producing substantial amounts ofheat and hydrogen to quickly achieve high operating temperaturesnecessary for startup, and is capable of producing substantial amountsof heat and hydrogen necessary to respond to dramatic increases inelectrical load demand on the fuel cell during transient conditions. Thepresent invention provides alternatives to and advantages over the priorart.

SUMMARY OF THE INVENTION

One embodiment of the invention includes the direct vaporization ofwater by combustor exhaust to create steam and charging the steam into afuel processor for rapid startup.

Another embodiment of the invention includes the direct vaporization ofwater by combustor exhaust to create steam, and charging the steam intoa fuel processor for rapid up-transients.

Another embodiment of the invention includes the use of cool, leanexhaust to increase mass flow for staged rich combustion within fuelprocessor reactors.

Another embodiment of the invention includes the use of cool, leanexhaust via water spray or heat exchange which therefore has reducedoxygen content and charging this exhaust into an autothermal reactor andtherefore allows fuel rich reaction in the autothermal reactor at oxygento carbon ratios greater than one as required to avoid carbon formationor fuel slip without creating excessively high temperatures that wouldotherwise occur without dilution at oxygen to carbon ratios greater thanone.

Another embodiment of the invention includes the use of steamcondensation to rapidly heat reactors and heat exchangers to thecondensation temperature to allow steam to pass through such reactorsand heat exchangers until steam can be produced using conventional steamgeneration components within the fuel cell system.

Another embodiment of the invention includes the use of directvaporization of water by combustor exhaust to produce steam and chargingthe steam into a water gas shift reactor to support water gas shiftreactions.

Another embodiment of the invention includes the use of directvaporization of water by combustor exhaust to produce steam, andcharging the steam into an autothermal reactor to support steamreforming and high-temperature shift reactions.

Another embodiment of the invention includes the use of directvaporization of water by fuel rich combustion exhaust to produce steam,H₂ and CO and charging the same into an autothermal reactor and the useof direct vaporization of water by combustor exhaust to produce steamwith excess O₂ and charging into a water gas shift reactor where theoverall fuel to air ratio upstream of a preferential oxidation reactoris slightly rich of stoichiometric conditions as this will produce a gascomposition with sufficient H₂ levels and low CO levels withoutrequiring water gas shift activity which is desirable to ensurepreferential oxidation catalyst light-off at ambient temperatureswithout CO blanketing of the catalyst.

Another embodiment of the invention includes the direct vaporization ofwater by combustor exhaust to produce a combustor effluent streamincluding combustion byproducts and steam, and charging of the combustoreffluent into a preferential oxidation reactor having a catalyst thereinso that the catalyst is heated to its light off temperature.

These and other objects, features and advantages of the presentinvention will become apparent from the following brief description ofthe drawings, detailed description of the preferred embodiments, andappended claims and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic illustration of a fuel cell system according tothe present invention;

FIG. 2 is a schematic illustration of the fuel cell system according tothe present invention; and

FIG. 3 illustrates a direct water vaporizing combustor according to thepresent invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 1 illustrates a fuel cell system 10 according to the presentinvention. In this preferred embodiment, the fuel cell system 10includes an inlet portion 12. A reformable fuel which may includecompounds or molecules including hydrogen, including, but not limitedto, gasoline, methanol, and/or methane is charged into the inlet vialine or plumbing 14. During normal operation of the fuel cell stack 32(that is, other than during startup or transient conditions as describedbelow), an oxidant such as oxygen in the form of air and/or steam may becharged into the inlet 12 via line or plumbing 16. The reformable fueland oxidant and/or steam are mixed in the inlet 12 and then charged (vialine or plumbing 13) into a fuel reforming reactor 18 downstream of theinlet 12. The fuel reforming reactor 18 may include a suitable catalystto reform the fuel and to produce a hydrogen-rich stream using a varietyof techniques as described above. The fuel reforming reactor 18 may be asteam reforming reactor having a suitable catalyst for reacting the fuelwith steam. The fuel reforming reactor 18 may also be a partialoxidation reactor including a suitable catalyst for promoting thereaction of the fuel with oxygen or air in proportions less than thatneeded for complete oxidation. The fuel reforming reactor 18 may also bean autothermal reforming reactor including a suitable catalyst forpromoting the partial reaction of the fuel with steam and the partialreaction of the fuel with oxygen or air in a combination steam reformingand partial oxidation type reactor. Suitable catalysts for these fuelreforming reactors are known to those skilled in the art, particularlythose in the catalyst art, and typically are precious metal basedcatalysts usually including platinum. A suitable autothermal reformingreactor may include precious metal based catalysts including platinum,rhodium, Ru and Pd, and may include additional promoters to promote thepartial oxidation and steam reforming reactions in the autothermalreactor. The catalyst may be coated on or impregnated in beads or asubstrate which may be a ceramic foam, ceramic or metal monolith, orplate type substrates. For an autothermal reforming reactor, thecatalyst is uniformly coated on the substrate; however, the front of theautothermal reactor predominantly promotes a partial oxidation reactionbecause the chemical kinetics of the partial oxidation reaction arefaster than the steam reforming reaction. Thus, most of the oxygen isconsumed in the front of the autothermal reactor and only steam isavailable in the rear of the reactor for hydrocarbon reforming.Therefore, the rear of the autothermal reactor predominantly promotesthe steam reforming reaction.

As described earlier, the effluent exiting via line 15 from the fuelreforming reactor 18 may have undesirably high concentrations of CO.Therefore, gas purification components may be located downstream of thefuel reforming reactor 18. The hydrogen-rich stream exiting the fuelreforming reactor 18 may optionally be charged via line or plumbing 15to a heat exchanger 20 to decrease the temperature of the hydrogen-richstream and heat the air and/or steam charged into the inlet 12 via lineor plumbing 16 for normal operation. The hydrogen-rich stream exitingthe heat exchanger 20 may optionally be charged via line or plumbing 17to the water gas shift reactor 22 having a suitable catalyst to reactthe hydrogen-rich stream with the steam charged into the water gas shiftreactor 22 via line or plumbing 26 and/or with excess steam in theeffluent from the fuel reforming reactor 18. Suitable catalysts for thewater gas shift reactor include precious metal-based catalysts such asPt, and non-precious metal-based catalysts such as CuZn and/or FeCr. Ineither case, additional promoters may be added to enhance the water gasshift reaction. Again, the catalyst is coated on or impregnated in beadsor a substrate as described above. As described above, the steam reactswith the CO to produce carbon dioxide and H₂, in the water gas shiftreactor.

The hydrogen-rich gas stream exiting the water gas shift reactor 22 maystill have too high of a concentration of CO. Therefore, thehydrogen-rich gas stream exiting the water gas shift reactor 22 may becharged via line or plumbing 19 to a preferential oxidation reactor 24having a suitable catalyst therein for promoting a preferentialoxidation of carbon monoxide to carbon dioxide. Suitable preferentialoxidation reactor catalysts include precious metals such as gold and/orplatinum. Again, additional promoters may be added to further enhancethe preferential oxidation reaction. The catalyst may also be carried inor on beads or substrates as described above. Additional oxidant in theform of air is charged via line or plumbing 28 to the preferentialoxidation reactor 24. As described above, the additional oxygen reactswith the CO to produce CO₂. The hydrogen-rich stream exiting thepreferential oxidation reactor 24 includes an acceptable amount of COwhich typically is 20-200 ppm, and preferably less than 20 ppm. Thehydrogen-rich stream with low CO is delivered via line or plumbing 30 toa fuel cell, and preferably a fuel cell stack 32 wherein the hydrogen isreacted with oxygen (providing via line or plumbing 34) to produceelectricity in a manner known to those skilled in the art.

The cathode exhaust from the fuel cell stack 32 may be charged via line80 to a combustion device such as a catalytic combustor 82. Likewise,the anode exhaust from the fuel cell stack 32 may be charged via line 84to the same combustor device 82 wherein the anode and the cathodeexhaust are combusted and the exhaust is charged to the atmosphere vialine 86 or used elsewhere in the fuel cell system 10.

For mobile applications, such as for use in automobiles, trucks and thelike, to facilitate rapid startup (when the system has not been running,components are cold, and the fuel cell is not producing electricity), asource of substantial heat and steam is needed in a very short period oftime. To facilitate rapid startup, the present invention provides afirst direct water vaporizing combustor 36 into which a combustible fuelis charged via line or plumbing 38 and into which in oxygen in the formof air is charged via line or plumbing 40. The first direct watervaporizing combustor 36 includes an ignition source such as a sparksource (sparkplug) as will be described hereafter for igniting the fuelin the presence of the oxygen (in the air) to produce a high temperatureexhaust stream. Water is also charged into the first direct vaporizingcombustor 36 via line or plumbing 42. The water in line 42 may beprovided from a water source such as a water tank 44. The water issprayed into the high temperature exhaust (produced by combusting thefuel) to immediately vaporize the water and produce a stream includingsteam and the fuel combustion byproducts. The steam and the fuelcombustion byproducts produced by the first direct water vaporizingcombustor 36 may be delivered via lines 46, 48, through a bypass valve49, through lines 50 and 52 to the heat exchanger 20 that is used toheat the effluent from the fuel reforming reactor 18 for startup. Fromthe heat exchanger 20, the stream including the steam and fuelcombustion byproducts is charged into the inlet 12 via line or plumbing16, and onward into the fuel reforming reactor 18.

If the water source used to spray water into the first direct watervaporizing combustor 36 is frozen, the bypass valve 49 is controlled todirect the hot exhaust from the first direct water vaporizing combustor36 via lines 46 and 54 to a second heat exchanger 56. The second heatexchanger 56 warms a heat exchange fluid that may be delivered in to athird heat exchanger 58 in the water tank 44 to thaw the frozen water.Alternatively, the steam from the first direct water vaporizingcombustor 36 may be charged via line 204 into a steam heat exchanger 206in the water tank and then discharged from the heat exchanger 206 vialine 208. The exhaust from the first direct water vaporizing combustor36 continues on via line 60, bypass valve 49, lines 50 and 52, throughthe heat exchanger 20 and charged to the inlet 12 via line 16. Light offhydrogen may be provided via line 62 and charged into line 52 andultimately into the fuel reforming reactor 18 via line 16. The hydrogenmay be provided by a pressurized hydrogen storage tank, oralternatively, the hydrogen may be stored in a hydrogen storage unit202. The hydrogen storage unit 202 may include a hydrogen storagematerial wherein hydrogen is adsorbed, absorbed or bonded to thehydrogen storage material. The hydrogen may be released from thehydrogen storage unit 202 upon application of heat from the steam or thecharging of the steam directly into or onto the hydrogen storagematerial. Accordingly, alternative embodiment includes a line 200 fromthe first direct water vaporizing combustor 36 to the hydrogen storageunit 202 to use steam to heat the hydrogen storage material using a heatexchanger (not shown) or the steam may be charged directly onto thehydrogen storage material. If a heat exchanger is used, the steam andcombustion byproducts would exit the hydrogen storage unit 202 via aseparate line (not shown) and then connect to line 52. In that case,only H₂ would be carried in line 62. If the steam and combustionbyproducts from the first direct water vaporizing combustor 36 arecharged directly into or onto the hydrogen storage material, line 62would include H₂, steam and combustion byproducts.

Water may be charged via line 66 to a third heat exchanger 68 in thepreferential oxidation reactor 24 to remove heat and produce steam whichmay be charged via line 70 into the steam line 52 that carries steamcreated by the first direct water vaporization combustor 36.

A second direct water vaporizing combustor 64 may be provided andcharged with a combustible fuel via line 72. The fuel is combusted inthe presence of oxygen provided by air charged into the second directwater vaporizing combustor 64 via line 74. Water is sprayed into thesecond direct water vaporization combustor 64 via line 76 to producesteam. The exhaust stream including steam and fuel combustion byproductsproduced by the second direct water vaporization combustor 64 is chargedinto the water gas shift reactor 22 via line 26. The stream includingsteam (26) and fuel combustion byproducts that is charged into the watergas shift reactor 22 is required to reduce the CO to levels ranging fromabout 1-2 mole percent which the PrOx reactor 24 can handle for final COcleanup before delivery to the fuel cell stack 32.

The sequential steps for starting the fuel cell system 10 illustrated inFIG. 1 from a cold start are as follows: (1) flowing air via line 40 tothe first direct water vaporizing combustor 36 and onward to fuelreforming reactor 18, and flowing air via line 74 to the second directwater vaporizing combustor 64; (2) delivering fuel via line 38 to thefirst direct water vaporizing combustor 36, and delivering fuel via line72 to the second direct water vaporizing combustor 64 and energizingsparkplugs in each combustor 36, 64 to ignite the fuel and oxygentherein; (3) delivering water via line 42 to the first direct watervaporizing combustor 36 to produce steam, and delivering water via line76 to the second direct water vaporizing combustor 64 to produce steam,so that the steam from the first direct water vaporizing combustor 36 ischarged into the fuel reforming reactor 18 and steam from the seconddirect water vaporizing combustor 64 is charged into the water gas shiftreactor 22; (4) delivering light off hydrogen (stored hydrogen orreformate) via line 62 to the fuel processing reactor 18; (5) deliveringair via line 28 to the PrOx reactor 24 and delivering air via line 34 tothe fuel cell stack 32; (6) determining when the catalysts in the fuelreforming reactor 18, water gas shift reactor 22, and preferentialoxidation reactor 24 are above their respective light off temperaturesor heated to a temperature to provide the desired activity, andthereafter turning off the light off hydrogen (line 62) and deliveringfuel to the fuel processing reactor 18 via line 14; (7) drawing currentfrom the fuel cell stack 32 when available; and (8) when steam (fromfirst direct water vaporizing combustor 36 through fuel reformingreactor 18 and heat exchanger 20) is available to the water gas shiftreactor 22, the fuel 72 and water 76 to second water vaporizingcombustor 64 may be shut off (and the air 74 may be continued as neededto maintain the desired reaction temperature in the water gas shiftreactor 22), and when normal operation steam (from the preferentialoxidation reactor/vaporizer 24 as shown) is available to the fuelreforming reactor 18, the fuel 38 and water 40 to first water vaporizingcombustor 36 may be shut off (and the air 40 would continue to providethe oxygen for a partial oxidation or autothermal reforming type fuelreforming reactor).

With regard to the above sequential steps for starting out the fuel cellsystem illustrated in FIG. 1, if hydrogen for catalyst light off is notavailable, stored reformate could also be used. If hydrogen or reformateare not available for catalyst light off, EHC heating could be used forsmall portions of the catalyst to allow light off. The EHC heating wouldpreferably be conducted prior to the first step outlined above tominimize the electric energy for heating. For systems without hydrogen,stored reformate or EHC heating, the configuration shown in FIG. 2 wouldbe used.

FIG. 2 illustrates an alternative embodiment of the fuel cell system 10according to the present invention which is similar to the fuel cellsystem illustrated in FIG. 1 but with a few variations. The embodimentillustrated in FIG. 2 is particularly well suited for systems wherestartup hydrogen (or stored reformate) is not available. In thisalternative embodiment (FIG. 2), the steam generated by the first directwater vaporizing combustor 36 travels through bypass valve 49, throughlines 50 and 16 and is charged directly into the fuel reforming reactor18 via inlet 12. This arrangement achieves direct and rapid heating ofthe fuel reforming reactor 18 catalyst to achieve light off. It isdesirable to quickly heat each of the catalytic reactors so thatreformate production can begin as soon as possible. To achieve PrOxcatalyst light off, low CO reformate is required because high levels ofCO can blanket the PrOx catalyst and suppress reactions. Accordingly,the first direct water vaporizing combustor 36 is operated slightly fuelrich, thereby producing exhaust gas that contains hydrogen and lowlevels of CO. Operation at high temperatures near stoichiometricconditions is possible with the direct water vaporizing combustor 36 toreduce temperatures before any downstream components. Furthermore,because the second direct water vaporizing combustor 64 provides steamdirectly to the water gas shift reactor 22, CO levels can be reducedfurther in the water gas shift reactor 22 before the effluent enters thePrOx reactor 24.

The sequential steps for starting out the fuel cell system 10illustrated in FIG. 2 would be the same as that for FIG. 1 except thatno hydrogen would be utilized (added) in the first direct watervaporizing combustor 36 exhaust stream. In other words, the sequentialsteps in starting up the fuel cell system 10 illustrated in FIG. 2 wouldbe as follows: (1) flowing air via line 40 to the first direct watervaporizing combustor 36 and onward to fuel reforming reactor 18, andflowing air via line 74 to the second direct water vaporizing combustor64; (2) delivering fuel via line 38 to the first direct water vaporizingcombustor 36 to run the combustor in a slightly fuel rich condition, anddelivering fuel via line 72 to the second direct water vaporizingcombustor 64 and energizing sparkplugs in each combustor 36, 64 toignite fuel and air therein; (3) delivering water via line 42 to thefirst direct water vaporizing combustor 36, and delivering water vialine 76 to the second direct water vaporizing combustor 64 to producesteam from each combustor 36, 64 and so that steam is charged from thefirst direct water vaporizing combustor 36 into the fuel reformingreactor 18 and steam from the second direct vaporizing combustor 64 ischarged into the water gas shift reactor 22; (4) delivering air via line28 to the PrOx reactor 24 and delivering air via line 34 to the fuelcell stack 32; (5) determining when the catalyst are above theirrespective light off temperatures or heated to a temperature to providethe desired activity, and thereafter delivering fuel to the fuelprocessing reactor 18 via line 14 and reduce fuel 38 to first directwater vaporizing combustor 36 to operate in lean condition (the excessair provides oxygen to fuel reforming reactor 18) and continue the water42 to provide steam; and (6) drawing current from the fuel cell stack 32when available; and (7) when steam (from first direct water vaporizingcombustor 36 through fuel reforming reactor 18 and heat exchanger 20) isavailable to the water gas shift reactor 22, the fuel 72 and water 76 tosecond water vaporizing combustor 64 may be shut off (and the air 74 maybe continued as needed to maintain the desired reaction temperature inthe water gas shift reactor 22), and when normal operation steam (fromthe preferential oxidation reactor/vaporizer 24 as shown) is availableto the fuel reforming reactor 18, the fuel 38 and water 40 to firstwater vaporizing combustor 36 may be shut off (and the air 40 wouldcontinue to provide the oxygen for a partial oxidation or autothermalreforming type fuel reforming reactor).

Transition to normal operation of the fuel cell system 10 can begin whensteam is being generated by the fuel processors conventional means suchas by the PrOx reactor 24 and the heat exchanger 68 so that steam isdelivered to the water gas shift reactor 22 by way of the fuel reformingreactor 18. Steam can be delivered by this conventional manner when theupstream reactors and heat exchangers are above the condensationtemperature. Steam generated by the first direct water vaporizingcombustor 36 would rapidly heat these upstream reactors to thecondensation temperature by the heat of vaporization as the steam fromthe combustor condenses. It would therefore be desirable to drain thecondensed water. Otherwise, the water would have to be re-vaporizedbefore the flow into the reactors could achieve normal operatingtemperatures which would delay a full efficiency operation.

With normal operation, when steam is being generated and delivered, fuelvia line 38, water via line 42, fuel via line 72 and water via line 76would be shut off to the first water vaporizing combustor 36 and to thesecond water vaporizing combustor 64 respectively. Air flowing via lines40 and 74 through the first direct water vaporizing combustor 36 and thesecond direct water vaporizing combustor 64 respectively would besignificantly reduced to maintain a desired reaction temperature in thefuel reforming reactor 18 and the water gas shift reactor 22,respectively. Air delivered via line 40 through the first direct watervaporizing combustor 36 would be used to supply air to the fuelreforming reactor 18 for normal operations. The air delivered via line74 to the second direct water vaporizing combustor 64 can be utilized tomaintain a desired temperature at the front of the water gas shiftreactor 22 via partial oxidation of the fuel (via line 14) travelingthrough the gas shift reactor 22 until the water gas shift reactorcatalyst is fully heated. For the configuration illustrated in FIG. 2,the air delivered via line 88 to the fuel reforming reactor 18 would beused for normal operation rather than the air delivered via line 40through the first direct water vaporizing combustor 36. Using airdelivered via line 88 allows the air to be heated by the heat exchanger20 for increased fuel processor efficiency.

The above fuel cell systems illustrated in FIGS. 1 and 2 can be used todirectly provide steam needed for rapid fuel processor up transients.Either the first or second direct water vaporizing combustors 36 or 64can be used to rapidly generate steam. Additional fuel, air and waterwould be provided to the combustors to generate the required exhaustflow energy to vaporized the spray water. If the first direct watervaporizing combustor 36 is used, excess combustor air would provideoxygen to the fuel reforming reactor 18. If the second direct watervaporizing combustor 64 is used, it would be operated at stoichiometricconditions to prevent additional heating during partial oxidation of thereformate and excess oxygen on the water gas shift reactor catalyst.

FIG. 3 is a schematic illustration of a direct water vaporizingcombustor 36 (64) useful in the present invention. The direct watervaporizing combustor 36 includes a first housing 92 defining acombustion chamber 94. Fuel may be delivered via line 38 to a fuelinjector 96 for spraying or atomizing the fuel into the combustionchamber 94. Air may be delivered via line 40 to the combustion chamber94. A spark source 108 such as a spark plug is connected to the housing92 to create a spark in the combustion chamber 94 to ignite the fuel inthe presence of the air and to produce a flame 110. A chamber separationwall 99 having an opening 112 therein is provided allowing thehigh-temperature (high heat content) exhaust from the fuel combustion toenter a second (water spray) chamber 100 defined by a second housing 98of the combustor 36. Water is delivered via line 42 to a water injector102 constructed and arranged to spray water into the second (waterspray) chamber 100 and allow the sprayed water to be instantaneouslyvaporized by the high-temperature exhaust from the combustion exhaust.This creates combustor effluent including the steam and the fuelcombustion byproducts that exits the second housing through outlet 104so that the combustor effluent stream may be delivered via line 46 tothe fuel reforming reactor 18 (as best seen in FIGS. 1-2). An opening106 may be provided in the second housing 98 to allow water that has notbeen vaporized to drain from the second (water spray) chamber 100. Thewater sprayed into the exhaust of the combustor 36, 64 helps to keep thetemperature of the combustor sufficiently low to prevent damage to thecombustor or other components in the fuel cell system. Unlike prior artboilers, tube and shell exchangers, or compact bar and plate-type heatexchangers, the combustors of the present invention are lightweightdevices of reduced mass capable of instantaneously producing steam, andthus are particularly well suited for mobile applications such as foruse in automobiles, trucks and the like that are powered at least inpart by fuel cell systems.

The direct water vaporizing combustor 36 illustrated in FIG. 3 is justone embodiment capable of directly vaporizing sprayed water without theuse of a heat exchanger to produce steam for use in a fuel reformingreactor or fuel reformate purification equipment according to thepresent invention. Although combustion in a combustor is utilized toinstantaneously vaporized the sprayed water, any other means ofinstantaneously producing steam by vaporizing sprayed water iscontemplated as within the scope of the present invention.

1. A fuel cell system comprising a fuel reforming processor having acatalyst therein constructed and arranged to produce a reformate streamincluding hydrogen and carbon monoxide, a water gas shift reactordownstream of the fuel reforming processor and wherein the water gasshift reactor includes a catalyst therein constructed and arranged toreduce the amount of carbon monoxide in the reformate stream, apreferential oxidation reactor downstream of the water gas shift reactorand wherein the preferential oxidation reactor includes a catalysttherein constructed and arranged to preferentially oxidize carbonmonoxide into carbon dioxide and to produce a hydrogen-rich stream, anda fuel cell stack downstream of the preferential oxidation reactorconstructed and arranged to produce electricity from the hydrogen-richstream, a first direct water vaporizing combustor constructed andarranged to combust fuel producing a high-temperature fuel combustionbyproduct exhaust and to produce steam from water sprayed into thecombustion byproduct exhaust and wherein the first direct watervaporizing combustor is plumbed to the fuel reforming reactor to chargesteam therein, and a second direct water vaporizing combustorconstructed and arranged to combust a fuel to produce a high-temperaturefuel combustion byproduct exhaust and to produce steam from watersprayed into the fuel combustion byproduct exhaust and wherein thesecond direct water vaporizing combustor is plumbed to the water gasshift reactor to charge steam therein.
 2. A fuel cell system as setforth in claim 1 further comprising a heat exchanger system having afirst heat exchanger constructed and arranged to receive an effluentstream from the first direct water vaporization combustor and having aheat exchanger in a water tank, and wherein water for spraying into thefirst and second direct water vaporizing combustors is carried in thewater tank, and the heat exchanger system further including a heattransfer fluid circulating between the first heat exchanger and the heatexchanger in the water tank.
 3. A fuel cell system as set forth in claim2 further comprising bypass plumbing connected to the first direct watervaporize combustor and a bypass valve in the bypass plumbing movable toa first position wherein the effluent from the first direct watervaporizing combustor is directed through the first heat exchanger and toa second position wherein the effluent from the first direct watervaporizing combustor bypasses the first heat exchanger.
 4. A fuel cellsystem as set forth in claim 1 further comprising a second heatexchanger positioned between the fuel reforming reactor and the watergas shift reactor, and wherein the first direct water vaporizingcombustor is plumbed to the second heat exchanger to heat reformatestream exiting the fuel reforming processor.
 5. A fuel cell system asset forth in claim 4 further comprising a third heat exchanger in thepreferential oxidation reactor and the third heat exchanger beingplumbed to the second heat exchanger to allow a heat transfer fluid toflow from the third heat exchanger to the second heat exchanger.
 6. Afuel cell system as set forth in claim 1 further comprising a catalyticcombustor downstream of the fuel cell stack positioned to combust anodeand cathode exhaust from the fuel cell stack.
 7. A fuel cell system asset forth in claim 1 wherein at least one of the first and second directwater vaporizing combustors includes a housing defining a combustionchamber, a fuel injector positioned to inject fuel into the combustionchamber, an air inlet position to inject air into the combustionchamber, an ignition source positioned to ignite air and fuel in thecombustion chamber, and a water injector positioned to spray water intoan exhaust stream produced from the combustion of fuel and air in thecombustion chamber.
 8. A fuel cell system as set forth in claim 1wherein at least one of the first and second direct water vaporizingcombustors includes a first housing defining a combustion chambertherein, a fuel injector positioned to inject fuel into the combustionchamber, an air inlet position to inject air into the combustionchamber, an ignition source positioned to ignite fuel and air in thecombustion chamber, a second housing defining a water spray chamber, awater injector positioned to spray water into the water spray chamber, achamber separation wall partially separating the combustion chamber andwater spray chamber, and the chamber separation wall having an openingtherein to allow exhaust produced from the combustion of fuel and air inthe combustion chamber to enter the water spray chamber.
 9. A fuel cellsystem as set forth in claim 8 further comprising a drain openingcommunicating with the water spray chamber to allow water to drain fromthe water chamber.
 10. A fuel cell system comprising: a fuel reformingreactor, a water gas shift reactor downstream of the fuel reformingreactor, and a fuel cell stack downstream of the water gas shiftreactor; a first direct water vaporizing combustor having a fuelinjector, an air inlet and water injector, and wherein the first directwater vaporizing combustor is plumbed to the fuel reforming reactor tocharge an effluent stream including fuel combustion byproducts and steamproduced in the first combustor into the fuel reforming reactor; and asecond direct water vaporizing combustor having a fuel injector, an airinlet and water injector, and wherein the second direct water vaporizingcombustor is plumbed to the water gas shift reactor to charge aneffluent stream including fuel combustion byproducts and steam producedin the second combustor into the water gas shift reactor.
 11. A systemcomprising: a fuel reforming reactor, and a water gas shift reactordownstream of the fuel reforming reactor; a first direct watervaporizing combustor having a fuel injector, an air inlet and waterinjector, and wherein the first direct water vaporizing combustor isplumbed to the fuel reforming reactor to charge an effluent streamincluding fuel combustion byproducts and steam produced in the firstcombustor into the fuel reforming reactor; and a second direct watervaporizing combustor having a fuel injector, an air inlet and waterinjector, and wherein the second direct water vaporizing combustor isplumbed to the water gas shift reactor to charge an effluent streamincluding fuel combustion byproducts and steam produced in the secondcombustor into the water gas shift reactor.